The Atomic Mass of Elements Is the Mass of One Mole of That Element, So

Mole/mole problems

6.02 X 1023 objects is one mole.

The atomic mass of elements is the mass of one mole of that element, so

23 grams is the mass of one mole of Sodium and 35.4 grams is the mass of One mole of chlorine.

The formula weight (formula mass) of a compound is the mass of one mole of that compound.

H2SO4 H 2 X 1.0 = 2.0 S 1 X 32.0 = 32.0 O 4 x 16.0 = 64.0 98.0 FW or the (molar mass) of Hydrogen Sulfate.

Practice Problems

1. 40.0 grams of Sodium is how many moles of sodium?

40.0 g x 1 mole Na = ? Answer = 1.739 or 1.74 mole 23.0 g Na of Na

2. 200.0 g of Ba is how many moles ?

3. 175.0 g of Cu is how many moles?

4 Other way around , 4.5 moles of iron is how many grams?

4.5 moles Fe x 55.8 g Fe = 251.1 g Fe 1 mole

5 6.25 moles of Zn is how many grams?

6. 5.6 moles of CaCl2 is how many moles of CaCl2 Moving on to balanced equations

2H2 + O2 → 2H2O

This can be read as Two molecules of hydrogen plus one molecule of oxygen yields two Molecules of water. OR

Two moles of hydrogen plus one mole of oxygen yields two moles of water.

Remember a balanced equation is a recipe so if I started 10 moles of hydrogen instead of 2. I would need 5 moles of oxygen and would make 10 moles of water.( same ratio).

Let’s try another

2 KClO3 → 2 KCl + 3 O2 If we start with 9 moles of KClO3 instead of 2.

How many moles of oxygen would be formed? Using factor label we do the following.

9 moles KClO3 x 3 moles O2 = 13.5 moles O2 2 moles KCLO3

Notice the moles given ( KCLO3) cancels out leaving moles looking for.( oxygen).

So what are we doing? Take the moles given and mult by moles looking for over moles given in the equation. Which says for every 2 moles KCLO3 that decompose 3 moles of Oxygens are formed.

9 moles given x 3 moles looking for( from balance equation) = moles looking At start 2 Moles given ( from the balanced equation)

Practice

1. Zn + 2 HCl → ZnCl2 + H2

If 8 moles of HCl react how many moles of hydrogen will be formed? I know it’s easy, but set it up as a factor label problem so you learn how! It won’t be easy later.

+2 2. 3 Cu + 2 Bi(NO3)3 → 3 Cu(NO3 )2 + 2Bi

If 15 Moles of copper react in the above equation, how many moles of bismuth Will be formed? 4. If 25.0 moles of aluminum dust is added to a solution of silver nitrate, how moles of silver could be recovered? Hint you have to write the balanced equation first.

5. C2H5OH + 3 O2 → 2 CO2 + 3 H2O

If 7.5 moles of alcohol is burned how many moles of water will be formed? Show factor label? Part 2 how many grams of water is this?

6. When 35 moles of Al2(CO3)3 decomposes, how many moles of carbon dioxide will be released?